Synthetic ceramic compositions have been well known for use in bone repair and bone void filling procedures. Ceramic granules have been widely used for such procedures. One benefit of using ceramic granules, such as calcium phosphate granules, is that once they are packed into placement in a bone void, an interconnected network of pores is created between the granules that allows for the penetration of fluids and new bone cells that can attach to the surfaces of the granules and begin remodeling and resorbing. One drawback to the use of ceramic granules is migration issues associated with the non-cohesive nature of a granulated mixture.
Synthetic ceramic cements have also been widely used in bone repair and bone void filling procedures. Typically the ceramic cements are composed of calcium sulfate and/or calcium phosphate based powders that can be mixed into a paste and injected to set in situ, or alternatively can be pre-cast into a desired shape and then placed in vivo. One advantage to using ceramic cements is that a relatively high volume of ceramic material can be placed into the bone void space. Additionally, the cement, once it has set, has a very low occurrence of migration from the implantation site. One drawback to the use of ceramic cements is that there is little to no porosity at the time of implantation, preventing fluids and new bone cells from penetrating into the cement construct, and further that ceramic cement does not provide an optimum osteoconductive scaffold for bone remodeling.
For example, US Pat. Appl. Publ. No. 2010/0249794 describes a cement system that contains calcium sulfate hemihydrate (CSH), monocalcium phosphate monohydrate (MCPM) powder, and β-tricalcium phosphate (β-TCP) powder that forms an injectable bone graft substitute cement upon mixing with an aqueous solution. However, due to the high percentage of fine powder, the cement described does not offer a three dimensional porous structure simultaneously when the system sets as a cement in vivo. The porous structure is developed only as the calcium sulfate dihydrate (CSD) resorbs.
Attempts have been made to combine both ceramic granules and ceramic cements into bone void filler. For example, U.S. Pat. No. 7,754,246 describes a bulk mixture of ceramic cement and calcium phosphate granules which when mixed with an aqueous solution can set as a non-porous monolithic construct having the granules serve as a “reticulated framework.” This mixture can either be preformed into a desired shape ex vivo and subsequently implanted, or mixed into a paste and injected/implanted such that the mixture can set in vivo. In either case, there is no porous network upon implantation until the calcium sulfate begins to resorb. Also the relatively high percentage of cement to granule results in a low percentage of calcium phosphate granules relative to the overall bone void space into which it was implanted. This presents less than optimum conditions for an osteoconductive scaffolding for new bone growth and remodeling.